The field is fugitive emissions control. In particular, an autonomous system and method of its deployment is provided for minimizing fugitive airborne emissions of harmful products emitted by industrial operations, such as electroplating.
Some electroplating processes, such as those used to chrome plate metal, are highly inefficient. U.S. patents cover some of these processes. U.S. Pat. No. 2,862,863, Apparatus for Electrolytic Production of a Metal Product from Fused Salts, to Griffith, Dec. 2, 1958, details a method for producing a metal derived from an electrolyte such as halides of the target metals. U.S. Pat. No. 3,104,221, Self Circulation Solution Anode for Chromium Plating Vessels, to Hill, Sep. 17, 1963 provides a method for chrome plating the interior of an article that may have one end completely enclosed. U.S. Pat. No. 4,933,061, Electroplating Tank, to Kulkarni et al., Jun. 12, 1990 describes an electroplating tank with a sparger system in the bottom of the tank for directing solution upward and a cathode rack for holding items to be plated intermediate anode plates.
These plating systems create byproduct gases that rise as bubbles and burst, emitting a mist of chromic acid to the atmosphere. These emissions must be addressed to meet federal pollution standards since hexavalent chrome is a carcinogen.
In chrome plating solutions, these chromic acid-forming bubbles rise and disperse uniformly on the surface of the electroplating solution, away from the plating process. To treat the particulates thus generated requires a sufficient ventilation flow to insure they are forwarded to and captured by scrubbing filters. A typically required ventilation flow is 200-250 ft3/min. of air per ft2 of plating tank surface (cfm/sf). Conventional large ventilation systems remove the mist to an area of treatment removed from the plating tanks. These systems include large hoods, connecting ductwork, and at least one blower. The remote treatment technology may be a composite mesh pad unit or a packed bed scrubber. The large ventilation system incurs a large part of the energy costs to treat the mist as well as requiring initial capital for installation and consuming valuable space in a work area.
One somewhat unconventional treatment system is the Venturi/Vortex scrubber described in U.S. Pat. No. 5,149,411, Toxic Fumes Removal Apparatus for Plating Tank, to Castle, Sep. 22, 1992. This system, designed to replace larger more conventional systems, captures plating bubbles using a vortex drain operating by gravity. It was designed to separate the liquid and gas phases, re-circulate the liquid and treat the gas before exhausting the treated gas to the atmosphere. Although a patent was granted on this system and method, it had practical limitations that prevented it from being adopted commercially. Hay, K. J. et al., Venturi/Vortex Scrubber Technology for Controlling/Recycling Chromium Electroplating Emissions, ESTCP Demonstration Project Final Report, Technical Report 99/43, U.S. Army Construction Engineering Research Laboratory (CERL), March 1999.
U.S. Pat. No. 5,766,428, Chromium Plating Solution, Solution Waste from Chromium Plating and Closed Recycling System for Chromic Acid Cleaning Water in Chromium Plating, to Iida, Jun. 16, 1998 describes a large complex system for cleaning the mists emitted that uses a final treatment means preferably located underground.
U.S. Pat. No. 3,985,628, Pollution Control in Electroplating Systems, to Myers, Oct. 12, 1976, provides a bulky complex means to scrub the emitted mist using plating rinsing water, claiming a transfer of xe2x80x9cchemical valuesxe2x80x9d to the water and water to the air. The resultant chemically enriched water is returned to the plating solution while no auxiliary air is added other than that required to xe2x80x9csweep overxe2x80x9d the plating baths.
Another concern with conventional electroplating tanks is their use of air circulation lines. Agitating (sparging) the plating solution with air bubbles near the plating activity ensures constant mixing of the solution thus yielding a uniform coating or plating. However, air bubbles thus generated increase surface emissions.
In view of the drawbacks associated with conventional plating systems, there is a need for a system and method that reduces costs associated with controlling fugitive emissions. A system and method of its use are provided for reducing the size of the costly, energy robbing ventilation system mandated to be installed over any open vessel emitting airborne hazards.
To minimize the energy burden in treating fugitive emissions from open vessels that contain material that may volatilize and escape, an autonomous system, termed an autonomous pushed liquid recirculation system (APLRS), and method of its use are provided. The APLRS includes a fluid intake to a conduit connected to a pump, the intake positioned in the vessel along a portion of a wall of the vessel and a fluid exhaust from a conduit connected to an opposite side of the pump, the exhaust positioned in the vessel along a portion of a wall of the vessel approximately opposite the position of the intake. In a preferred embodiment, this configuration provides an equal path within the vessel from the pump to the intake and the pump to the exhaust. Because the APLRS depends on its location within the vessel in relation to fluid therein, it also incorporates a novel multi-part float that enables the APLRS to maintain an adequate geometry and position for fulfilling its function.
The dimensions of the vessel in which a preferred embodiment of the present invention may be employed include a tank having a length longer than its width, but also may include square, round, oval or polygonal shapes other than rectangular.
As compared to existing conventional fugitive emissions control systems and methods, an embodiment of the APLRS reduces ventilation requirements for electroplating tanks, thus reducing both capital equipment and operating (energy) costs.
The reduction in size and energy cost is effected through a reduction in the bubbles that arise to the surface of the vessel during industrial operations, such as electroplating. Fewer bubbles bursting on the surface reduce the amount of required forced ventilation.
A preferred embodiment of the APLRS meets the above goals by using jets of liquid to produce a uniform cross flow, i.e., a xe2x80x9cpush,xe2x80x9d near and across the surface of liquid in a vessel such as an electroplating tank. This pushes any bubbles arising to the surface of the vessel to one side of the vessel. These bubbles then cluster at a wall of the vessel due to not being able to resist the induced flow of the jets of liquid originating from an opposite wall.
This results in an effective reduction in the vessel""s surface area since all of the bubbles are no longer dispersed over the entire surface but rather xe2x80x9cpushedxe2x80x9d to one side. In a preferred embodiment this side is a long side of the vessel because of the advantages of exploiting the physics of inducing the flow across the narrowest part of the vessel.
While controlling the location and area in which bubbles may burst, another advantage of the APLRS is the inducing of a natural recirculation of solution within the vessel. This leads to more efficient and uniform plating in those vessels employed in plating operations, for example. This may eliminate or reduce the need for a separate air sparger to achieve this function.
Further, in a preferred embodiment of the APLRS, the bubbles are xe2x80x9cpushedxe2x80x9d to a controlled collection point prior to becoming a fugitive emission, unlike existing emissions control systems that capture resultant mist in a xe2x80x9cpush-pullxe2x80x9d air system only after a bubble has burst and become a fugitive emission anywhere on the surface of liquid in the vessel.
Thus, provided is an autonomous pushed liquid recirculation system for use with open systems containing hazardous materials that may be volatized. A preferred embodiment of the present invention will operate independently of the fluid level maintained in a vessel in which it is installed. This capability is enabled by a novel float system incorporated in the design of the APLRS.